The effects of growth media, temperature, pH and light on the development of four isolates of Coniothyrium minitans (CONIO and CH8 (colony type 3), G4 (colony type 4) and G9 (colony type 5)) were examined. Conidial germination, pycnidial production and hyphal extension rate were initially studied on seven different agar-based growth media at 18–20 °C. Potato-dextrose agar (PDA) and malt extract agar (MEA) consistently gave the greatest conidial germination, pycnidial production and hyphal extension rate for all four isolates. Growth and development on molasses-yeast agar was equivalent to that on PDA and MEA except that hyphal extension rate was slower. Subsequently, the effects of temperature, pH and light on the development of C. minitans were investigated on PDA only. The temperature range of conidial germination and pycnidial production of the four isolates was between 10–25° with the optimum at approximately 20°. Hyphal extension occurred over a greater temperature range, between 4 and 25°, with a maximum extension rate of approximately 3·5 mm d−1 for all isolates occurring between 20–25°. Conidial germination, pycnidial production and hyphal extension occurred over a pH range between 3–8 with optimum values for all growth assessments occurring between pH 4·5 and 5·6. Increasing light period from continuous dark, to 12 h light/12 h dark or continuous light had no effect on conidial germination or extension growth, but significantly increased pycnidial production.

Isolates G4 and G9, previously characterized by sparse production of pycnidia in comparison with CONIO and CH8, consistently exhibited a reduced production of pycnidia on all media, at all temperatures and pH ranges, and all light regimes tested. This demonstrates the stability of this character among these isolates of C. minitans. The significance of these results for improving production of inoculum of this biocontrol agent and in the identification and classification of isolates of C. minitans is discussed.